Process for recovery of phosphate minerals



United States Patent P PROCESS FOR RECOVERY OF PHOSPHATE MINERALS Homer E. Uhland, Lakeland, Fla., assignor to International Minerals & Chemical Corporation, a corporation of New York No Drawing. Application November 29, 1954, Serial No. 471,890

11 Claims. Cl. 209-166) to flotation plants in which latter stages the material is treated in aqueous slurry form. This slurry contains sizable amounts of silica, socalled colloidal phosphates, and clays normally delineated as slimes, as well as other gangue materials. In thefflotation operation the phosphate is recovered in as pure a form as possible and is substantially free of slimes. In a flotation process the phosphate particles must be of such a size that they may be economically treated.

As an initial step in obtaining a flotation slurry, the ore material is subjected to a preliminary washing operation wherein a sizable quantity of the coarse phosphatic values are removed by a screen operation which produces a pebble product containing all of the +1 mm. values. The -1 mm. values containing the phosphatic particles, silica particles, and the slimes as a slurry must be further processed to give maximum recovery of the granular material and substantially complete removal of the slime material which if allowed to remain would adversely affect the subsequent concentration process, i. e., silica removal.

A rough separation of the slime material may be accomplished in a number of ways. As practiced commercially in the phosphate fields of Florida, recourse is taken to a hydro-separation or hydrocyclone process. The overflow from this hydroseparator or classification system is withdrawn and sent to a settling or slime pondJ This overflow is made up chiefly of suspended clay and extremely fine particles of phosphate, i. e., particles of a suflicient degree of fineness that they could not be economically recovered at any subsequent step of the process. This separation is commonly made, in the phosphate field, at approximately 150 or 200 mesh. The coarser fraction, essentially -l mm. and +150 mesh, is separately withdrawn. Following removal of this fraction, it is sized further; usually by hydraulic classification or screening at about mesh to about 48 mesh. The coarserfraction (i. e. -1 mm. +35 mesh) is then treated for removal of the phosphate values on agglomerate tables, spirals, belts, underwater screens or by froth flotation. The finer fraction (i. e. -35 150 mesh) is then subjected'to froth flotation operations. A

In the froth flotation operation reagents are employed to float selectively a desired constituent of the ore. If the desired constituent isphosphate, then such reagents as fuel'oil, kerosenealong with long chain fatty acids and caustic soda, fatty acid' soaps andthe like are used.

Patented Nov. 12, 1957 In general, the concentrates from rougher flotation steps are subjected to scrubbing with chemical agents to remove flotation reagents and then to secondary flotation operations which float the minor constituents of the concentrates. In the case of phosphate flotation, the reagents utilized in the secondary flotation areamines derived from long chain fatty acids or salts thereof such as the. acetate salt. This secondary flotation operation floats the minor constituent of the concentrate, which at this stage of phosphate flotation procedure is silica. Amines and their salts, while effective as flotation reagents for silica, are nevertheless not highly selective, i. e., are not effective depressants for phosphates. As a consequence, considerable quantities of phosphate material are floated together with the silica, and this phosphate material is lost in the silica tail which is sent to waste. j

Presence of the amine reagent has proven an eifective barrier to re-reagentizing the silica tail with agents which would be selective for phosphate flotation. Further, the removal of the amine reagents by chemical means has proven expensive and entirely unsatisfactory.

It is a primary object of this invention, therefore, to overcome the shortcomings and disadvantages of the process heretofore in use.

It is a further object of this invention to teach a process wherein the secondary reagents are removed so that the tail fractions may be resubjected to flotation with reagents selective to the desired constituents of the concentrate.

It is still another object of this invention to provide a process wherein amine reagents used in the secondary flotation operations for phosphate are effectively removed from the tail fraction. 7

It is still another object of this invention to provide a process wherein higher recovery of phosphate is attained due to the removal of amine reagents, which then permits the reworking of the tail to recover phosphate constituents heretofore lost to waste.

These and other objects of the invention will be obvious to those skilled in the art from a study of the process hereinafter outlined in detail.

Now it has been discovered that the amine reagents present on products recovered in amine flotation operations, which amines heretofore have not been susceptible of economic removal and which interfere with subsequent conditioning of products with anionic reagents and with subsequent attempts at flotation for improvement of the recovery of a desired component, can be cheaply and effectively removed by mixing the amine flotation product in slurry form with so-called slime materials and agitating the mixture. During agitation the amine reagents are transferred to the slime particles. The mixture is next subjected to wet classification separations to remove the slime material from the flotation product solids. The deslimed solids may then be conditionedwith anionic reagents for flotation, and the desired components which would be lost as a result of discarding the amine flotation product may be recovered by flotation in a concentrated form.

More in detail, the method as applied to the processing of Florida pebble phosphate ore comprises, generally speaking, transfer of the matrix as mined from thenatural deposit in slurry form. This slurry contains sizeable amounts of silica clay and miscellaneous gangue material, as well as phosphate particles in various forms and particle size. Phosphate particles having a diameter of approximately +1 mm. are removed from the slurry by a washing and screening operation and marketed as pebble. The 1 mm. material is subjected to hydroseparation or other wet classification operation. The overflow product from the hydroseparator constitutes the so-called slimes of the system and is made up chiefly of dissolved and suspended clay and so-calledcolloidal phosphate, i. e., phosu) phate of a particle size of the same order of magnitude as the suspended clays.

Underflow solids from the hydroseparation step are subjected to beneficiation processes such as froth flotation tdfree'the phosphate of silica and minor amounts of gangue material in order to produce a phosphate coricen trate, preferably of about 74% to about 78% bone phosphate of lime content if the character of the rock is such a'sto permit production of such a grade.

i In the froth flotation operation reagents are employed depending upon the constituent which is to be floated. in a typical phosphate operation the first stage flotation utilizes carboxyl-containing negative ion agents such as are found in the mixture of fuel oil, kerosene, and long chain fatty acids as well as caustic soda. This mixture characterized by the fatty acids generally denominated anionic agent flotation froths up and floats away a predominantly phosphate material as concentrate.

An effective way to upgrade the phosphate concentrate further is to subject it to a cationic or positive ion agent flotatiqn, which process floats the silica and leaves a phosphate concentrate as the underflow product. Before conditioning the phosphate concentrate with cationic agents, the anionic agent 'or agents are removed from the first cpncentrate by scrubbing it with about a 20% sulfuric acid solution. The language scrubbing as used in wet mineral processing means agitating the solids in slurry form generally in a solids content of about 45% to about 75% solids. After scrubbing the phosphate concentrate, the acid solution is removed in dewatering and washing steps. Concentrate solids are then slurried in water and conditioned with amines or salts of amines derived from long chain fatty'acids such as primary monoamines derived from' hydrogenatedtallow, fatty acids or from soya fatty acids, N-dodecylamine, N-hexadecylamine, etc.; diamines or salts of diamines such as lauryl fatty diamine or so'ya ,fatty diamine acetate.

Under current operating procedures, the amine tail productis sent to waste with from about 10% to about 45% bone phosphate of lime content. In a plant processing'500 tons per hour of underflow solids from the hydro separator this percentage of B. P. L. material constitutes an appreciable loss. In the new process as applied to phosphate ore processing, this amine tail product generally in slurry form is mixed with the overflow slimes from the above described hydroseparation operation. The'invention at this stage will immediately suggest two modes'of operation. In the first modification this amine tailproduct'is delivered to the above described hydroseparation operation wherein slimes are removed on a continuous recycle basis. In the second and preferredmod'e of operation, the amine tail product is mixed with overflow slimes in proportionsgiving a resultant slurry having' about /s% to about 5% by weight of slime'solids. Slimes are generally incorporated into the amine tails product by adding between about and about 100 gall ons per minute of slime slurry which corresponds to the addition of approximately 2 pounds to approximately 20 pounds of slime solids per ton of amine tail solids. The resultant slurry is agitated at about 50% to about 70% solids content for between about 30 seconds and about 180 seconds, with an optimum period of about '90 seconds to about 130 seconds preferred. Slimes which preferentially take up or adsorb the amine reagent are removednom contact with the tail solids by classification io'r hydroseparation'or hydrocyclone operations.

Deslimed silica tail material is next conditioned with aniouic reagentg for example, the tall oil kerosene mixture used for the flotation of the original phosphate concentrate together with fuel oil and caustic soda. Flotation of the conditioned, tail product gives a recovery of about 90% to about 98% of the .phosphatein the tail. This secondary concentrate can be refloated toproduce a product of between about 2% to about 8% acid insoluble 4 material combinable with the initial phosphate concentrate.

The amount of negative and positive ion agents which are employed in the flotation steps which are an integrated part of the instant novel process may vary according to the phosphatic or silicidus content of the ore. The amount of negative ion agent which is employed to produce a flotation concentrate may vary over a fairly wide range, but between about 0.4 pound and about 2 pounds of negative ion agent per ton of solids in the flotation pulp has been found to be particularly advantageous. When conducting a flotation operation in the presence of positive ion agent, for example, long chain aliphatic amines or their water soluble acid addition salts, the amount of suchreagent may vary over fairly wide limits but between about 0.2 pound and about 1 pound of such reagent per ton of ore based upon the solids content of the reagentized pulp is conveniently employed. The amount of frothing and other agents, such as pine oil, kerosene, fuel oil, etc., which is optionally but generally present during flotation may also vary over fairly wide limits, between about 0.1 pound and about 1 pound per ton of solids in a flotation pulp. The type of reagent employed will be particularly effective within certain pH ranges, for example, the negative ion agents are generally effective in the alkaline pH range. Negative ion reagents selected from the group comprising fatty acids, resin acids, tail oil, naphthalene acids, soaps of these reagents, etc. are particularly effective when conducting a flotation operation at a pH in the range between about 7 and ab.o.ut 9. The invention is not limited to such reagents, but any reagent which has an aflinity for phosphate valuesrnay be employed similarly. Reagents other than longchain aliphatic amines or their water soluble acid addition salts are effective at pHsin the range between about 3 and about 6. It will be obvious to those skilled in the art of flotation that the selectivity of any particular reagent or mixtures of several reagents is not usually suflicient to achieve a complete recovery of the desired component in any one flotation operation. It is, therefore, within the scope of the invention to recycle various pulp streams from any particular flotation operation wheth'er this will be a rougher or a cleaner flotation.

The invention will be better understood from the following description and examples.

EXAMPLE I A phosphate rock such as the type found in the phosphate pebble fields of central Florida is subjected to a washing operation in order to remove slimes and organic matter. The washed rock in an aqueous pulp is subjected to screening or hydraulic sizing operation whereby the largerv particles of rock are segregated from material which is -35 mesh particle size. The material remaining after the pebble has been removed, which consists of phosphate, clay, silica and the like, is further treated by hydroseparation to overflow the. fine particles normally discarded from the system as slimes and to recover underflow particles which are 'thenconditioned in an aqueous pulp containing about 60% solids with about one pound per ton of ore solids, the reagent comprising about 75% tall oil and about25% kerosene. About 3 pounds of fuel oil is added to thefmi'xture and sufficient caustic soda is added to give the mixture a pH in the. range of between about 8.5 to about 9.0. The resultant pulp is then subjected to a flotationo'peration at a solids content of about 30% by weight in a Denver laboratory machine and a float recovered containing. approximately 60% tricalcium phosphate, the balance being silica and silicious gangue. This phosphatic concentrate is scrubbed with about 2 pounds of sulfuric acid (60 B.) per ton of solids in order to remove the reagents therefrom. The acid-treated product is washed until it is substantially neutral and is then conditioned in an, aqueous pulp with a mixture of long chain aliphatic amines, the latter comprising a mixture of about 73% mono-octadecylamine and about 24% mono-hexadecylamine, together with small quantities of secondary and tertiary amines whose aliphatic groups contain between about 12 and about 18 carbon atoms. This reagent can be added in the form of an acid addition salt. The conditioned concentrate is then subjected to a flotation operation at a solids content of about 30% in a Denver laboratory floation machine. The float product from this operation is a predominantly silica material, i. e., the product contains approximately 85% of the silica originally in the concentrate and has an approximately bone phosphate of lime content.

EXAMPLE n Amine reagent flotation tail (silica float product from Example I) was washed and watered. Equal portions of this washed product were conditioned in an aqueous pulp of approximately 60% solids with about 0.5 pounds of reagent per ton of silica product treated; the reagent comprising approximately 75% tall oil and 25% kerosene by weight. About 3 pounds of fuel oil and sufficient caustic soda was added to give the conditioned pulp a pH ofv between 8.5 to 9.0 in each instance. Each conditioned pulp was then subjected to flotation at a solids content of approximately 30% by weight in a Denver laboratory flotation machine to produce a flotation product and a phosphate concentrate product. The phosphate concentrate products produced were attrition scrubbed with about 2 pounds of sulfuric acid (60 B.) per ton of solids. This acid treated product was washed until it was substantially neutral 'and then conditioned in an aqueous pulp with a long chain aliphatic amine. The results obtained at two diflerent amine concentrations are shown in the following table:

From Table 1 it is clear that the amine tail phosphate cencentrate is not susceptible to beneficiation to an economic product of industry.

EXAMPLE in A portion of the amine flotation tail producedfrom Example I was mixed with slime material in proportions of 20 gallons of the hydroseparator overflow slurry to one ton of amine tail product. This corresponds to adding approximately 5 pounds of slime solids per ton of amine tail product. The solids mixture was agitated in an upright centrifugal mixer for two minutes and then deslimed by decantation. The dewatered solids were pulped with water and the aqueous pulp containing about 60% solids conditioned with about 0.5 pound of reagent per ton of solids the same as in Example II. The other accessory reagents and the subsequent flotation also were identical to that given the sample in Example II. The flotation product in this test was then given an amine flotation again identical to Example II. The results obtained on this test are shown in Table 2.

The underflow product (phosphate concentrate) pro= duced on these tests is acceptable to industry as an economic product.

Having thus fully described and illustrated the character of the invention, what is desired to be secured and claimed by Letters Patent is:

1. The method of removing cationic amine reagents from flotation separation products which were concentrated with the aid of said amine reagents which comprises mixing in slurry form the flotation product containing amine reagent and a slime material, agitating the mixture and subjecting the mixture to a wet classification operation to separate the slime material containing adsorbed amine reagents from the flotation products.

2. The method of removing cationic amine reagents from phosphate flotation products which were concentrated with the aid of amine reagents which comprises mixing the tail product containing amine reagent with slime material originally present in the ore, agitating the mixture and subjecting the mixture to a wet classification operation to separate the slime material containing adsorbed amine reagents from the tail product.

'3. The method of improving the recovery of desired components of ore's which are concentrated with the aid of cationic amine reagents comprising mixing in slurry form flotation operation products containing amine reagent with slime material, subjecting the slurry mixture to agitation and wet classification to separate slime material containing adsorbed amine reagent, subjecting the deslimed flotation product to a further flotation operation with anionic reagents and then subjecting the anionic reagent concentrate to flotation with cationic reagents to recover a concentrate of the desired component.

4. The method of improving the recovery of phosphate from Florida pebble phosphate ore which comprises mixing in slurry form the silica tail product obtained by means of amine reagent flotation with slime material originally present in the phosphate ore, subjecting the slurry mixture to agitation and wet classification to separate the slime material containing adsorbed amine reagent, subjecting the dewatered silica tail product to flotation with anionic reagents and then subjecting the anionic reagent concentrate to flotation with amine reagent to recover a phosphate concentrate.

5. In a process of concentrating minerals wherein an ore in a liberated state is first subjected to a flotation operation employing carboxyl-containing negative ion flotation agent and the flotation product is subjected to a second flotation operation employing nitrogenous positive ion flotation agent, the improvement comprising slurrying a product from the nitrogenous positive ion flotation operation with slime material originally present in the ore, agitating the slurry mixture, removing the slime material from the flotation product by separative treatment, conditioning the deslimed product with carboxyl-containing negative ion reagent, subjecting the conditioned material to a froth flotation operation to recover a beneficiated fraction of the ore, and subjecting the beneficiated fraction to a final froth flotation operation.

6. The method of improving the recovery of desired components of ores which are concentrated with the aid of cationic amine reagents comprising mixing in slurry form flotation operation products containing amine reagent With slime material having a particle size of less than about mesh to about 200 mesh standard screen size, subjecting the slurry mixture to agitation and wet classification to separate slime material containing adsorbed amine reagent, subjecting the deslimed flotation product to a further flotation operation with anionic reagents and then subjecting the anionic reagent concentrate to flotation with cationic reagents to recover a concentrate of the desired component.

7. The method of improving the recovery of desired components of ores which are concentrated with the aid of cationic amine reagents comprising mixing in slurry form .flotation operation products .containinglamine re: agent with slime material having a particle sizeof less than about 150 mesh to about 200 mesh standard screen size, said slime material being added in quantities in the range between about 2 pounds and about 20 pounds of slime solids per ton of amine float product, agitating the slurry mixture for a period of about 90 seconds to about 130 seconds, subjecting the slurry mixture to wet classification to separate slime material containing adsorbed amine reagent, subjecting the deslimed flotation product to a further flotation operation with anionic re.- agents and thenisubjecting the anionic reagent concentrate to flotation with cationic reagents to .recover a concentrate .of the desired component.

8. The method of improving the recovery of phosphate from Florida pebble phosphate ore which comprises mix: ing in slurry form the silica'tail product obtained by means of an amine reagenttflotation with slirnes removed from the ore prior to flotation, removing the slimes and conditioning the product with carboxyl-containing negative ion reagent, subjecting the conditioned material to a froth flotation operation to recover a phosphate fraction and subjecting the phosphate fraction to a final flotation operation with a long chain aliphatic amineacid addition salt.

9. The method of improving the recovery of phosphate from Florida pebble phosphate ore which comprises wet classifying the ore to remove the low density fraction slimes therefrom, subjecting the slime free ore to a flotation operation at a pH in the range between about 7 and about 9 for the concentration of phosphate values with carboxyI-containing negative ion agent, subjecting the phosphatic concentrate tov a silica flotation operation with a long chain aliphatic amine-acid addition salt, recirculating the amine flotation tail to the wet classification operation where the amine reagent is adsorbed by the slimes and floated away from the ore solids,

10. The process of recovering phosphate from Florida pebble phosphate. one containing slimematerial wherein concentration of vphosphate values with carboxyl-contain-- ing negative ion agent, subjecting the phosphatic float to a silica flotation operation with a long chain aliphatic amine-acid addition salt, adding to the silica float a portion of the 200 mesh slime material, classifying the: slurry mixture to remove the slime material containing: adsorbed amine reagent from the amine tail solids, sub-- jecting the amine tail solid to a flotation operation at a. pH between about 7 and about 9 for the concentration of phosphate values with carboxyhcontaining negative ion agent, and subjecting this fraction to a silica flotation operation with a long chain aliphatic amine-acid addition salt to recover a concentrate rich in phosphate material.

11, The method of improving the recovery of desired components of ores which are concentrated with the aid of cationic amine reagents comprising mixing in slurry form flotation separation products containing amine reagent with siime material, subjecting the slurry mixture to agitation and wet classification to separate slime material containing adsorbed amine reagent, and subjecting. the deslimed flotation product to a further flotation operation with anionic reagents to recover a concentrate of the desired component,

Lawver Oct. 21, 1952 Duke et al; July 10, 1956 

1. THE METHOD OF REMOVING CATIONIC AMINE REAGENTS FROM FLOTATION SEPARATION PRODUCTS WHICH WERE CONCENTRATED WITH THE AID OF SAID AMINE REAGENTS WHICH COMPRISES MIXING IN SLURRY FORM THE FLOTATION PRODUCT CONTAINING AMINE REAGENT AND A SLIME MATERIAL, AGITATING THEE MIXTURE AND SUBJECTING THE MIXTURE TO A WET CLASSIFICATION OPERATION TO SEPARATE THE SLIME MATERIAL CONTAINING ADSORBED AMINE REAGENTS FROM THE FLOTATION PRODUCTS. 